1. Field of the Invention
The present invention relates to a nucleic acid purification method and purification apparatus and particularly to the purification method and purification apparatus suited to separate nucleic acid contained in the biological sample from the coexisting substance and to take it out.
2. Description of the Prior Art
A great number of gene technologies have been developed due to progress of molecular biology, and many pathetic genes have been separated and identified by such technologies. As a result, In the field of medical treatment as well, a technique of molecular biology is adopted in the diagnosis or inspection method. This makes it possible to perform the diagnosis which is extremely difficult so far and to achieve a substantial reduction in the number of days for inspection.
Such a progress is attributable to commercial application of gene amplification method, especially, polymerase chain reaction (called PCR method) in many respects. The PCR method makes it possible to amplify nucleic acid in the solution sequence-specifically. For this reason, it indirectly proves existence of a very small number of viruses present in the serum, by amplifying and detecting the nucleic acid as genes of these viruses. However, there are some problems when this PCR method is used for clinical applications in daily examinations. Especially, extraction of nucleic acids in the pretreatment process and purification process are important to maintain accuracy. Some techniques have been proposed regarding purification of nucleic acid.
According to the method disclosed in Japanese Official Patent Gazette 266864/1999, a nucleic acid capturing tip incorporating solid phase containing silica is used to extract nucleic acid automatically. A nozzle tip is mounted on the liquid suction/discharge movable nozzle and sucks from the bottle the binding enhancer to accelerate nucleic acid to be bound onto said solid phase. Then it sucks the sample containing nucleic acid from the specimen vessel and discharge their mixture into the reaction vessel. After the mixture has been discharged, the nozzle tip is discarded, and a new nucleic acid capturing tip is mounted in position. The mixture is sucked from inside said reaction vessel and discharged into the nucleic acid capturing tip connected to the liquid suction/discharge movable nozzle. Then nucleic acid in the sucked mixture is bound with the solid phase in the nucleic acid capturing tip, and liquid in said nucleic acid capturing tip is discharged. Then washing solution discharged in the washing vessel is sucked into said nucleic acid capturing tip, and said washing solution is discharged from said nucleic acid capturing tip. Said solid phase bound with nucleic acid and interior of said nucleic acid capturing tip are washed. Further, eluent is sucked into the said nucleic acid capturing tip after having been washed, and eluent containing the nucleic acid separated from said solid phase is discharged into a vessel for purified product.
According to the method disclosed in Japanese Official Patent Gazette 266864/1999, when there is reaction between the sample containing nucleic acid and various types of reagents, the sample containing nucleic acid is sucked from the specimen vessel or reaction vessel and is dispensed into the targeted reaction vessel. So said sample may scatter up to the mechanism holding the nozzle tip, and may cause contamination which will give a serious influence to nucleic acid purifying performances.
The solid phase bound with nucleic acid and the interior of the nucleic acid capturing tip are washed. The washing solution discharged into special-purpose vessel is sucked into said tip and is discharged into the special-purpose vessel. This process is repeated, resulting in a poor cleaning efficiency. Further, if washing solution remains in the solid phase of said tip, the next eluent concentration will be affected to deteriorate nucleic acid purifying performances.